Thin film electroluminescent (TFEL) display panels offer several advantages over other display technologies such as cathode ray tubes (CRTs) and liquid crystal displays (LCDs). Compared with CRTs, TFEL display panels require less power, provide a larger viewing angle, and are much thinner. Compared with LCDs, TFEL display panels have a larger viewing angle, do not require auxiliary lighting, and can have a larger display area.
FIG. 1 shows a prior art TFEL display panel. The TFEL display has a glass panel 10, a plurality of transparent electrodes 12, a first layer of a dielectric 14, a phosphor layer 16, a second dielectric layer 18, and a plurality of metal electrodes 20 perpendicular to the transparent electrodes 12. The transparent electrodes 12 are typically indium-tin oxide (ITO) and the metal electrodes 20 are typically Al. The dielectric layers 14, 18 protect the phosphor layer 16 from excessive dc currents. When an electrical potential, such as about 200 V, is applied between the transparent electrodes 12 and the metal electrodes 20, electrons tunnel from one of the interfaces between the dielectric layers 14, 18 and the phosphor layer 16 into the phosphor layer where they are rapidly accelerated. The phosphor layer 16 typically comprises ZnS doped with Mn. Electrons entering the phosphor layer 16 excite the Mn causing the Mn to emit photons. The photons pass through the first dielectric layer 14, the transparent electrodes 12, and the glass panel 10 to form a visible image.
Although current TFEL displays are satisfactory for some applications, more advanced applications require brighter higher contrast displays, larger displays, and sunlight viewable displays. One approach in attempt to provide adequate panel contrast under high ambient illumination is the use of a circular polarizer filter which reduces ambient reflected light. While this approach may provide reasonable contrast in moderate ambient lighting conditions, it also has a number of drawbacks which include a high cost and a maximum light transmission of about 37%.